6o 



BOTANY AND J'llARMACOGNOSY. 



spores are greenish or yellowisli in color, varionsly sculptured 

 and vary from 0.025 '"'^i- ^o 0.1^8 mm. in diameter. 



Fern Groups. There are a number of distinct groups of 

 ferns which vary considerably in appearance. ( i ) In the Tropics 



Fig. 36. Male fern [Aspidium (Nephrodium or Dryopleris) Filix mas\. A, portion 

 of leaflet showing a number of more or less reniform sori near the mid- vein; B, transverse 

 section through a ripe sori showing clusters of stalked sporangia, which are covered by 

 the indusium (i), an outgrowth of the leaflet; C, a closed but ripe sporangium showing the 

 annulus or ring (n), and the irregular-shaped spores within; D, showing the manner of 

 opening of the mature sporangium and the dispersal of the spores; E, two spores much 

 magnified. After Dodel-Port. 



as well as in greenhouses tree ferns, characterized by an over- 

 ground stem, occur. The leaves arise at the summit of the stem 

 or trunk and form a crown. 



